This invention relates to a method for operating a portable data carrier and to such a portable data carrier. In particular, the invention relates to a method for operating a chip card or a chip module, and to such a chip card or such a chip module.
Portable data carriers in the form of chip cards having a processing unit, also called microprocessor chip cards or processor cards, are used in many security-critical areas, for example as identity documents, for proving a subscriber's access authorization, e.g. for a mobile radio network, or for carrying out funds transfer transactions. Such use of the chip card is frequently effected in interaction with a terminal device provided for the particular application, which is configured for accessing security-critical data of such a chip card after an authentication has been effected.
When security-critical applications are carried out by a portable data carrier, for example a chip card, it is necessary to protect the portable data carrier and the security-critical data deposited therein, such as cryptographic keys, from attacks and unauthorized tampering.
Various attack methods are known by which physical parameters of the portable data carrier are measured during the program execution in order to make inferences about security-critical data, in particular cryptographic keys, that are employed upon the program execution. For example, in simple power analysis (SPA) the power consumption of the portable data carrier during the run of a program routine is measured and examined. In differential power analysis (DPA), in contrast, the power consumption over many program runs is evaluated statistically.